This invention relates in general to compensating for errors in the trajectory of reentry bodies and, in particular, to a method for compensating for such errors which utilizes a maneuvering reentry body. It is well known that the theoretical trajectory of ballistic missiles can be predetermined with great accuracy. Consequently, the so-called "nominal" position of the missile at any time in flight following booster burnout can be predicted. However, because of errors generated by the weapon delivery system, the standard deviation of the weapon system delivery dispersion at nominal reentry time is described in the trajectory plane by the inclined ellipse. Conventional fuzing subsystems utilize combinations of impact fuzing, fuzing at a radar measured altitude, and fuzing at a predetermined time after encountering a given longitudinal deceleration level. With these fuzing techniques, the dispersion ellipse is propagated along the trajectory to yield an elongated downrange-cross-range ellipse at the fuzing location. The downrange dispersion caused by errors generated in the weapon delivery system limits the predictable effectiveness of the ballistic reentry body upon target.
One approach for reducing the downrange errors generated in the delivery system is described in U.S. Pat. No. 3,990,657. In this approach, the downrange error is reduced by determining the altitude error from the nominal at a particular time during flight, computing a position error from this altitude error, and then maneuvering the reentry body in flight to return the reentry body to its nominal trajectory. In a second approach, described in U.S. Pat. No. 4,456,202, the deviation from the nominal trajectory is also detected by in-flight measurements. In this approach, however, the fuzing location is adjusted to compensate for the error in trajectory. Both approaches require an on-board radar for measuring the altitude of the reentry body.